I am trying to understand why one party should alert (get a green light mayhaps?!) the others in the case of a paralel project...
because it could piss someone off? Weird reason.
The reason at least in my opinion is not because sbdy will get pissed off but
Il2 modding scene is quite active yes, but again it has a finite potential for producing a number of aircraft in a given amount of time. And from the modding scene even fewer are willing to make aircraft due to the complexity required.
So making double projects is a choice and I fully respect that, but it is a pretty inneffective way to proceed since he might have another idea to make that is not being worked on atm and provide a whole new aircraft instead of a different version.
Or better still if both sides are interested they could also cooperate and make an aircraft with more details/work in it.
Saying that if he still does not want to do that and just wants to make his own version it's his choice and I have no right to tell him what to do ofc.